The present invention relates to a new and improved additive for mortar and concrete in the form of aqueous dispersions.
Substances are already known to the art which improve the plasticity, the workability as well as the pumping properties of mortar and concrete. There are especially used derivatives of cellulose, such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose. Also there have already been utilized ethylene oxide polymers, polyvinyl alcohol, polyglycol, sulfonated melamine formaldehyde resins, polyacrylic amide and similar substances for such purpose.
What is disadvantageous is that all of the aforementioned products only can be utilized in a powder state. When using such products in powder form considerable difficulties arise since the substances are hygroscopic. The absorption of water from the air, which can amount to 45%, can bring about an adhesion or binding of the powder dosing installation. When using these substances in a dry state, there is additionally present the possibility of dust explosions. A further disadvantage resides in the fact that with the small additive quantities of about 50 grams per 2.5 tons concrete an exact dosing is associated with difficulties owing to the continuous absorption of water from the air.
The aforementioned swellable additive substances are water-soluble polymers which owing to hydration of their structural layers gradually transform into highly viscous solutions. Owing to this property of forming with water highly viscous solutions, wherein it should be mentioned that in 2% solutions there have been measured viscosities up to 100,000 centipoises (cps) and for practically employed additives there are required concentrations of at least 10% and viscosities under 200 cps, these additive agents cannot be employed as solutions.